Faculty Bibliography

A point mutation of G to C at codon 693 of the amyloid-beta (Abeta) precursor protein gene results in Glu to Gln substitution at position 22 of the Abeta (AbetaQ22) associated with hereditary cerebrovascular amyloidosis with hemorrhage Dutch type. Factors that regulate AbetaQ22 levels in the central nervous system (CNS) are largely unknown. By using ventriculo-cisternal perfusion technique in guinea pigs, we demonstrated that clearance from the cerebrospinal fluid and transport from the CNS to blood of [(125)I]-AbetaQ22 (1 nM) were reduced by 36% and 52%, respectively, in comparison to the wild type Abeta(1-40) peptide. In contrast to significant uptake and transport of Abeta(1-40) across the brain capillaries and leptomeningeal vessels, AbetaQ22 was not taken up at these CNS vascular transport sites, which was associated with its 53% greater accumulation in the brain. The CNS clearance of Abeta(1-40) was half-saturated at 23.6 nM; AbetaQ22 had about 6.8-fold less affinity for the CNS efflux transporters and its elimination relied mainly on transport across the choroid plexus. Thus, the Dutch mutation impairs elimination of Abeta from brain by reducing its rapid transport across the blood-brain barrier and the vascular drainage pathways, which in turn may result in accumulation of the peptide around the blood vessels and in brain

Cerebral amyloid angiopathy defines the deposition of amyloid fibrils in the walls of medium- and small-size leptomeningeal and cortical arteries and arterioles. This condition is an important cause of cerebral hemorrhages and is also associated with cerebral infarctions and diffused white matter changes. In many instances, vascular amyloid deposits co-exist with intraneuronal neurofibrillary tangles, being the cognitive areas the most severely affected. However, the importance of cerebral amyloid angiopathy as a causative element in the process of neurodegeneration is still debatable. This review discusses inherited dementia syndromes associated with neuronal loss and amyloid deposition in the brain, with particular focus on familial Alzheimer's disease and chromosome 13 dementia. (c) 2002 Prous Science. All rights reserved

Abeta1-42 vaccination trials were recently terminated because of cerebral inflammation, which may be due to Abeta toxicity and/or autoimmunity. Abeta forms inflammatory/toxic fibrils, may seed fibril formation and crosses the blood brain barrier (BBB) in experimental animals. Because of attenuated immune response, the elderly may not clear injected Abeta1-42, which may then initiate and/or enhance amyloid angiopathy and plaque formation. Therefore, it is safer to use immunogenic Abeta derivatives, which are less likely to be toxic. Unlike Abeta1-42, K6Abeta1-30 is non-fibrillogenic and non-toxic in human cell culture but diminishes amyloid burden to a similar extent as reported for Abeta1-42. Additionally, ramified IL-1beta positive microglia, associated with the plaques, are absent in the immunized mice indicating reduced inflammation in these animals. We are currently comparing the therapeutic potential of these two compounds in alum adjuvants, which are approved for human use. Our behavioral findings in a year old Tg2576 mice show no difference between these groups and controls in various sensorimotor tasks, linear maze and water maze. However, in the radial arm maze, vaccinated Tg mice and their non-Tg littermates performed equally well and had fewer errors than Tg controls (p=0.008). These groups are being evaluated at a higher amyloid burden and subsequently their brain pathology will be assessed. Overall, the use of nontoxic Abeta derivatives and/or Abeta clearing compounds with very limited access into the CNS, such as IgM, may prove to have reduced side effects compared to Abeta and/or IgG-based immunization

Neurodegenerative conditions are increasing in prevalence as the average human life expectancy rises. Alzheimer's disease (AD) is the fourth commonest cause of death in the United States; the recent outbreak of new variant Creutzfeldt-Jakob disease (nvCJD) has raised the specter of a large population being at risk to develop this prionosis. The pathogenesis of many neurodegenerative diseases is now recognized to be associated with abnormalities of protein conformation. A common theme in these disorders is the conversion of a soluble normal precursor protein into an insoluble, aggregated, ?-sheet rich form that is toxic. In AD, a critical event is the conversion of the normal, soluble A? (sA?) peptide into fibrillar A?, within neuritic plaques and congophilic angiopathy (1). Similarly, in the prionoses, the central event is the conversion of the normal prion protein, PrPC, to PrPSc (2). An increased ?-sheet content characterizes both A? and PrPSc.

Familial British dementia (FBD), pathologically characterized by cerebral amyloid angiopathy (CAA), amyloid plaques, and neurofibrillary degeneration, is associated with a stop codon mutation in the BRI gene resulting in the production of an amyloidogenic fragment, amyloid-Bri (ABri). The aim of this study was to assess the distribution of ABri fibrillar and nonfibrillar lesions and their relationship to neurofibrillary pathology, astroglial and microglial response using immunohistochemistry, confocal microscopy, and immunoelectron microscopy in five cases of FBD. Abnormal tau was studied with immunoblotting. We present evidence that ABri is deposited throughout the central nervous system in blood vessels and parenchyma where both amyloid (fibrillar) and pre-amyloid (nonfibrillar) lesions are formed. Ultrastructurally amyloid lesions appear as bundles of fibrils recognized by an antibody raised against ABri, whereas Thioflavin S-negative diffuse deposits consist of amorphous electron-dense material with sparse, dispersed fibrils. In contrast to nonfibrillar lesions, fibrillar ABri is associated with a marked astrocytic and microglial response. Neurofibrillary tangles and neuropil threads occurring mainly in limbic structures, are found in areas affected by all types of ABri lesions whereas abnormal neurites are present around amyloid lesions. Immunoblotting for tau revealed a triplet electrophoretic migration pattern. Our observations confirm a close link between ABri deposition and neurodegeneration in FBD

Variant human cystatin C (L68Q) is an amyloidogenic protein. It deposits in the cerebral vasculature of Icelandic patients with cerebral amyloid angiopathy, leading to stroke. Wild-type and variant cystatin C are cysteine proteinase inhibitors which form concentration dependent inactive dimers; however, variant cystatin C dimerizes at lower concentrations and has an increased susceptibility to a serine protease. We studied the effect of the L68Q amino acid substitution on cystatin C properties, utilizing full length cystatin C purified in mild conditions from media of cells stably transfected with either the wild-type or variant cystatin C genes. The variant cystatin C forms fibrils in vitro detectable by electron microscopy in conditions in which the wild-type protein forms amorphous aggregates. We also show by circular dichroism, steady-state fluorescence and Fourier-transformed infrared spectroscopy that the amino acid substitution modifies cystatin C structure by destabilizing alpha-helical structures and exposing the tryptophan residue to a more polar environment, yielding a more unfolded molecule. These spectral changes demonstrate that variant cystatin C has a three-dimensional structure different from that of the wild-type protein. The structural differences between variant and wild-type cystatin C account for the susceptibility of the variant protein to unfolding, proteolysis and fibrillogenesis

The BRI3 gene is a member of the BRI gene family, made up of at least three different genes (BRI1-3). Previous studies established the cDNA sequence and structure of the human and mouse BRI1 and BRI2 genes and we recently reported that mutations in the BRI2 isoform, located on chromosome 13, are associated with dementia in humans. In the present work, we determine the complete cDNA sequence and genomic organization of the human BRI3 gene. BRI3 codes for a polypeptide of 267 amino acids, with a Mr of 30 KDa and a pI of 8.47. The amino acid sequence is 43.7% identical to the sequence of the human BRI2, and 38.3% identical to that of human BRI1, with the highest percentage of amino acid identity being concentrated on the C-terminal half of the molecules. In Northern blots, BRI3 cDNA hybridizes only one message of approximately 2.1 kilobases, which is predominantly present in the human brain. The BRI3 gene is localized on chromosome 2 and consists of six exons spanning more than 20 kb. Homology search of EST data banks retrieved a Caenorhabditis briggsae homolog of BRI, indicating that the BRI gene belongs to a strongly conserved gene family. These studies, aimed at characterizing the members of the BRI gene family, may provide valuable clues to the understanding of their normal function and how mutations in BRI2 can cause neurodegeneration and dementia similar to Alzheimer's disease

Inheritance of apoE4 is a strong risk factor for the development of late-onset sporadic Alzheimer's disease (AD). Several lines of evidence suggest that apoE4 binds to the Alzheimer Abeta protein and, under certain experimental conditions, promotes formation of beta-sheet structures and amyloid fibrils. Deposition of amyloid fibrils is a critical step in the development of AD. We report here that addition of melatonin to Abeta in the presence of apoE resulted in a potent isoform-specific inhibition of fibril formation, the extent of which was far greater than that of the inhibition produced by melatonin alone. This effect was structure-dependent and unrelated to the antioxidant properties of melatonin, since it could be reproduced neither with the structurally related indole N-acetyl-5-hydroxytryptamine nor with the antioxidants ascorbate, alpha-tocophenol, and PBN. The enhanced inhibitory effects of melatonin and apoE were lost when bovine serum albumin was substituted for apoE. In addition, Abeta in combination with apoE was highly neurotoxic (apoE4 > apoE3) to neuronal cells in culture, and this activity was also prevented by melatonin. These findings suggest that reductions in brain melatonin, which occur during aging, may contribute to a proamyloidogenic microenvironment in the aging brain